If there's one thing Democratic former Rep. Brad Schneider wants voters in Illinois' 10th District to know, it's that incumbent Rep. Robert J. Dold has sided with Republicans in Congress.

The narrator in one of Schneider's most recent ads repeats the phrase "Dold and the Republicans" four times. The phrase flashes on screen more times than that.

The ad, entitled "Facts," references Dold and the Republicans in the same breath because it's paid for by both the Schneider campaign and the Democratic Congressional Campaign Committee. Because the ad contains equal references to Dold and the party, the campaign and the committee split the cost of what's known as a "hybrid ad."

It's a relatively rare technique that differs from a coordinated ad, in which party committees are allowed to spend money on behalf of a candidate — subject to a federal limit.

This hybrid strategy, which has been employed by both parties, saves the party committees and the campaigns money since neither is paying for the full cost of the ad.

The cost-splitting helps the campaigns, which are subject to tighter contribution limits than the parties. And it helps the committees, which get to air partisan messages for the cheaper ad rate usually charged to candidates.

These ads don't work everywhere, and even where they do, their partisan messaging is not always a perfect fit.

Just last week, the Human Rights Campaign, which has endorsed Dold, criticized Schneider and the DCCC's ad for associating Dold with House Republicans' rejection of LGBT anti-discrimination employment protections.

Rules for how these ads should be constructed are murky to nonexistent. But cost-splitting between campaigns and committees is generally understood to be proportional to the space and time granted to the candidate versus the party.

To good government watchdogs, though, the technique raises red flags about skirting coordination and contribution limits that the FEC has never fully addressed.

A 12-year-old innovation

The practice dates back to 2004, when President George W. Bush's campaign split the cost of $81.4 million in television spending with the Republican National Committee.

That spending was on top of the legal maximum of $16 million in coordinated expenditures the RNC made for the Bush-Cheney campaign.

The spending didn't count toward the coordinated spending limit because the campaign reimbursed the party for their half of the ads.

With references like "President Bush and our leaders in Congress" or "John Kerry and liberals in Congress," the ads contained generic partisan messaging that — the party argued — justified its sharing the cost of the ad.

Combing through their opponent's FEC reports, the Democrats soon caught on to the practice and starting doing it too. The Kerry-Edwards campaign split $22 million in ads with the Democratic National Committee.

At the time, presidential campaigns were publicly funded, and that funding came with a limit on how much the campaigns could spend. By splitting the cost of an ad with the party, the Bush and Kerry campaigns were allowing their campaign dollars to go further.

Public financing is no longer in vogue, but the purpose of splitting the costs remains the same, said Paul Ryan, deputy executive director at the Campaign Legal Center, who has argued against the practice to the FEC.

Campaigns have smaller contribution limits than parties, so "offloading costs onto the party," Ryan said, allows the campaigns to tap into greater sources of money.

It doesn't always work

Congressional campaigns have been using hybrid ads since 2006, but there's a limit to where they are effective.

Schneider's "Facts" ad is all about party. So are two otherhybrid ads his campaign and the DCCC split the cost of in 2014. Schneider lost to Dold by less than 3 points that year.

Democrats hope that partisan message resonates in a place like Illinois' 10th District, where Democrats have a partisan advantage that makes Dold vulnerable. President Barack Obama twice carried this district by double digits.

"It's one of the few districts where the [other] party is unpopular enough where you can make the party argument and it works," said a Democratic operative who's worked on hybrid ads. Democrats would never employ the technique in Nebraska's 2nd District, for example, where vulnerable Democratic Rep. Brad Ashford is defending a Republican-leaning district and has been trying to downplay his party identification.

Where the technique runs into problems is when the blanket partisan messaging doesn't quite fit with the targeted candidate.

Schneider and the DCCC tied Dold to House Republicans on many issues, from raising the retirement age to cutting environmental protections and defunding Planned Parenthood.

But given that Dold is the only House Republican endorsed by the Human Rights Campaign, it was more of a stretch to lump Dold in with House Republicans on gay rights. "Dold and the Republicans even said employees could be fired, just for being gay," the narrator says in the ad.

What's the law?

The FEC solicited comments from the parties and groups like the Campaign Legal Center on the hybrid ad technique in 2007, but never issued any rules on the practice.

It has weighed in on related practices. In a 2006 advisory opinion requested on behalf of the Washington Democratic State Central Committee, the FEC concluded that candidates and parties could split the cost of direct mail that promotes a "clearly identified federal candidate" and generically promotes other candidates from the same party.

The identified candidate must pay at least 50 percent of the mailer — and proportionally more if he or she takes up more space. An FEC regulation on phone banking set a similar precedent for splitting costs for calls that reference a specific candidate and generically refer to others.